1. Field of the Invention
The present invention relates to an apparatus which includes a variety of assemblages which enable the apparatus to determine in situ the real evapotranspiration of a plant cover, such as cultivated land. The apparatus is also capable of determining the carbon dioxide exchange between the cultivated land and the atmosphere. Finally, the apparatus of the invention enables one to measure the hydrous state (moisture content) of the ground around the irrigated land.
2. Description of Material Information
In attempting to determine the biological status and needs of a plant cover, such as a farmed surface, it is necessary to monitor various environmental parameters, such that remedial action can be taken to maintain the farmland in peak condition. Among the environmental parameters that are important are the net water loss (evapotranspiration) of the ground cover (crop) to the atmosphere, the net exchange of carbon dioxide, and the hydrous state of the ground. In particular, the study of the evapotranspiration of cultivated land allows one to determine the water needs of the land, as well as the biochemical status of the particular vegetation involved.
In calculating the value of the evapotranspiration, it is known to apply the Bowen ratio method. This method consists in determining the net radiation, the conduction flux in the ground, and the differences of dry and wet bulb temperatures at two levels above the plant cover.
French patent application No. 79 17306 (now French Pat. No. 2,460,475), by the present Applicant, discloses an automatic evapotranspiration measuring apparatus which makes possible the use of the Bowen ratio method.
A second method of measuring the real evapotranspiration of a plant cover is known as the simplified combined aerodynamic method. The application of this method requires that the real evapotranspiration be calculated from the net radiation measure, the flux of the ground heat, the gradient of the temperature in the air, and the speed of the wind above the plant cover.